In diesel engines, very high injection pressures of up to 1,000 bar and above are aimed for in order to improve fuel preparation and to reduce the formation of pollutants. The demand for improved emissions and fuel economy is driving the industry toward higher injection pressures and shorter injection duration. In general, a steep injection curve at the beginning of injection is typical, and a sharply delimited end to injection is demanded.
Injection systems which are primarily mechanical in operation are generally used for such high-pressure injection. In this case, the fuel is compressed at the beginning of the injection process at a pumping element and the pumping energy is transmitted to the injection nozzle.
The fuel injection requirements of an engine are determined by the required engine performance parameters such as emissions, fuel economy, etc. Once the fuel injection requirements are determined, the load requirement of the mechanical system is determined. The mechanical system is then designed to fulfill such a load requirement. The fuel injection systems for modern diesel engines are required to produce very high injection pressures of up to a few thousand bar. The mechanical system is also required to produce a typically steep injection curve at the beginning of injection and a sharply delimited end to injection. These requirements lead to a mechanical system which produces highly transient, nearly impulse-like, short duration loads. A consequence of these loads is that the fuel injection drive shaft must sustain torque loads that are very cyclical, of very high magnitude, and which may reverse sign during the injection event. As the fuel injection requirements become more demanding, the injection drive shaft loads increase further.
The torque loads produced by such fuel systems create torsional vibration in the fuel injection drive system. This torsional vibration causes the meshed teeth of the timing gears to bounce or clash back and forth against each other through the backlash therebetween. This bouncing and clashing produces an objectional noise known as gear rattle. Not only does such torsional vibration cause impacts in the fuel system drive gears, but these impacts further excite the entire engine structure to vibrate, thus producing high levels of exterior noise. These gear impacts can cause excessive gear wear and failures, as well as substantially increased overall engine noise levels.
There is therefore a need in the prior art for a device that will substantially lessen the torsional vibration produced by the fuel injection drive system and thereby lower engine noise levels and vibration. The present invention is directed toward meeting these needs.